Is there a safety issue with Li-ion batteries?

The Dell laptop battery recall may presage an industry-wide or larger problem …

Laptop battery recalls are not a new idea, but Dell's recent offer to replace over 4 million of the devices has focused the spotlight on what could become an expanding area of concern. Since the spectacular photos of a Dell laptop bursting into flames surfaced in June, the problem of overheating laptop batteries has begun to garner attention outside of the computer industry. At the heart of the issue are two possibilities: either the lithium-ion (Li-ion) cells themselves are problematic, or the design of the battery packs using the cells is faulty.

The battery packs at the center of the Dell maelstrom contain cells manufactured by Sony, and their battery packs using cells from other sources have for now been deemed safe. Those Sony cells, however, are not only used by Dell, but by other computer manufacturers as well. If the cells are indeed found to be the malfunctioning component, the Li-ion manufacturing process itself may need to be reexamined.

Before we go any further, it needs to be emphasized that our purpose here is not to incite panic. There will be plenty of opportunity for local TV news programs to do that when the November ratings period rolls around. The fact is, out of millions of laptops shipped each quarter, only a miniscule percentage ever overheat, and fewer still burst into open flame. That said, Lithium-ion cells have become increasingly popular in recent years, and are now powering everything from cell phones to Segways. If there is a genuine issue with Li-ion cells, that increased popularity portends more recalls and injuries to come.

Although slightly more expensive to produce, the popularity of Li-ion cells stems from a number of advantages they have over other rechargeable technologies such as nickel cadmium (NiCd) and nickel metal hydride (NiMH). For one thing, Li-ion cells have a lower rate of self discharge than the competition, meaning that they are likely to retain much of their charge even after months of storage. For another, Li-ion cells have a higher energy density and usually produce a higher voltage per cell, meaning that a Li-ion battery pack can be smaller and lighter, while lasting longer and producing more "kick."

However, a potential failure can arise if—during the Li-ion manufacturing process—metal particles are allowed to contaminate the interior of the cells. Over time, those particles can move into the separator, which is an insulating barrier between the anode and cathode sides of the cell. That creates a short circuit between anode and cathode, allowing electrons to flow freely and quickly, and the battery fails.

Most of the time, that failure will consist of little more than the battery powering down and ceasing to function properly. In rare instances, the battery will overheat, then melt, catch fire, or even explode.

Even if it's a very rare occurrence, a prospective fire in one's lap should be taken seriously, and Dell was right to issue the recall. Unfortunately for some Dell users, the delivery schedule for their replacement battery packs may range as high as 75 days, which seems like a long time to wait if your laptop may burst into flames.

Update: Thanks to the many Ars faithful who pointed out that I was using the wrong shorthand for lithium-ion. I can always count on you to keep me honest. -Pete